FIG. 1 shows an example conventional battery system 100 (including management and control), such as for plug-in hybrid electric vehicles (PHEV) or hybrid electric vehicles (HEV). Cells are connected in parallel to form a battery set. For example, each cell possesses 3.3V for the case of lithium iron phosphorous battery cells. Sixteen (16) battery sets connected in series comprise a battery module, such as battery modules 102 (e.g., in the example of FIG. 1, assumed as each having a value of 52.8 volts (V)). Six (6) battery modules 102 connected in series (to motor 110) comprise, in this example, a portion of the battery system 100 having a cumulative voltage value of 316.8V (e.g., 52.8×6). Conventionally, each battery set of each battery module 102 is monitored and controlled directly by a vehicle electrical control unit (ECU) 104. The ECU 104 is coupled over a controlled area network (CAN) bus interface 106 to a module monitor and controller 108 associated with each battery module 102. In this example, a vast amount of data is transmitted for monitoring (e.g. voltages for each battery set) and control (e.g., battery set balancing, such as implemented by known cell balance devices that keep the battery sets balanced in capacity) as necessary. The resulting battery system 100 may become cost ineffective (e.g., complications in monitoring) and/or vulnerable to the conditions of the environment (e.g., electromagnetic interference (EMI)) that may make the electrical vehicle (EV), HEV, or PHEV unreliable.
A more advanced battery system 200 is shown in FIG. 2, where the control and monitoring of the battery system 200 is divided into master 202 and slave levels 204. The interface between the ECU 104 and the master level 202 comprises a CAN bus interface 106, whereas the interface between the master 202 and slave levels 204 comprises an RS485 interface 206, as one example among others. In this example system, most of the monitoring is dealt by slave-level control. However, data transmission is still inevitable via RS485 206 and/or CAN 106 between the master/slave and master/vehicle ECU, which may create reliability problems especially after a long service time.